1. Field of the Disclosure
Embodiments disclosed herein relate generally to an apparatus and method for hanging and supporting downhole devices. Other embodiments relate to supporting a liner hanger, and cementing and packing off a liner within a wellbore. Specific embodiments relate to a slip assembly having an expandable slip ring and gripping members that displace outwardly into engagement with the surface of a surrounding tubular.
2. Background Art
Typically, in the drilling of a well, a borehole is drilled from the earth's surface to a selected depth and a string of casing is suspended and then cemented in place within the borehole. A drill bit is then passed through the initial cased borehole and is used to drill a smaller diameter borehole to an even greater depth. A smaller diameter casing is then suspended and cemented in place within the new borehole. Generally, this is repeated until a plurality of concentric casings are suspended and cemented within the well to a depth which causes the well to extend through one or more hydrocarbon producing formations.
Oftentimes, rather than suspending a concentric casing from the bottom of the borehole to the surface, a liner may be hung either adjacent the lower end of a previously suspended and cemented casing, or from a previously suspended and cemented liner. A liner hanger is used to suspend the liner within the lower end of the previously set casing or liner. A setting tool disposed on the lower end of a work string is releasably connected to the liner hanger that is coupled with the top of the liner. The liner hanger, liner, setting tool, and other components are generally part of a liner hanger assembly.
Another component, such as a liner top packer, may also be part of the liner hanger assembly, which may be used to seal the liner in the event of a poor cement job or to prevent gas flow while the cement sets. Typically, the liner top packer is set down on top of the liner hanger, and the packer is set by the setting tool to seal the annulus between the liner and the previously set casing or liner. Liner top packers run with liner hangers typically include a tubular member with a bore in it that is coupled with the top end of the packer.
This tubular member is commonly referred to as a polished bore receptacle (“PBR”) or a tieback receptacle (“TBR”). Because the liner does not run to the surface, the liner hanger has the ability to receive the PBR or TBR to connect the liner with a string of casing that extends from the liner hanger back to the surface. There is typically a seal or seal stack between the PBR and the body of the packer that allows axial motion of the PBR relative to the liner top packer body. A standard seal stack includes a plurality of annular spaced seals that fit within the interior of the PBR. Often, a PBR is coupled into an upper end of the packer, and production tubing is stung into the PBR with an appropriate seal to prevent leakage between the interior of the PBR and the production tubing.
In operation, the work string lowers the liner into the portion of the wellbore that extends below the lower end of the previously set casing or liner. The liner hanger typically is lowered into the wellbore until the liner hanger is adjacent the lower end of the previously set casing or liner, and the lower end of the liner is above the bottom of the open borehole. Those of ordinary skill in the art will appreciate that it is desirable to have the inside diameter of the liner be as large as possible to allow more space for additional liners to be disposed within the well and to facilitate production.
When the liner reaches the desired location relative to the bottom of the open borehole and the previously set casing or liner, an anchor mechanism is actuated to move slips on the anchor mechanism from an original position to a displaced position, and into engagement with the previously set casing or liner. Once engaged with the surrounding surface, the anchor mechanism supports the weight of the liner hanger, a liner top packer, or both.
Typically, liner hangers and liner top packers use an anchor mechanism that may be actuated either hydraulically or mechanically. For example, a liner top packer often uses an anchor mechanism commonly referred to as a slip and cone assembly. In this manner, cone-shaped members are usually configured above and below the slips in such a way that the cones are moved toward each other to expand the slips outwardly into frictional engagement with the surrounding casing.
However, these slips sometimes displace outward prematurely before the anchoring mechanism is in place, thus the liner hanger assembly may anchor in the wrong location in the wellbore. Other times, as the liner hanger assembly is run into the wellbore, the slips may catch against downhole surfaces, which can cause damage to the anchor mechanism. In addition, when the anchor mechanism is set, the slips may break apart from a slip ring as the cones displace the slips outwardly. The slip assembly will then require removal from the wellbore for repair or replacement.
Accordingly, there exists a need for an improved slip assembly that may avoid pre-setting while running.